1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device. More particularly, the present invention relates to a liquid crystal display (LCD) device and a method for manufacturing the same, wherein ball spacers are fixedly used to reduce touch and press defects, and the content of a solid mixed with balls is increased to partially widen an area of the upper surface of the spacer to thereby prevent damage of the substrate that faces the spacer or of the structure provided on the same.
2. Discussion of the Related Art
With the progress of information-dependent society, the demand for various display devices has increased. To meet such a demand, efforts have recently been made to research flat panel display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), electro-luminescent displays (ELDs) and vacuum fluorescent displays (VFDs). Some types of such flat panel displays are being practically applied to various appliances for display purposes.
Of these, LCDs are currently most widely used as substitutes for cathode ray tubes (CRTs) in association with mobile image display devices because LCDs have advantages of superior picture quality, lightness, slimness, and low power consumption. Various applications of LCDs are being developed in association with not only mobile image display devices such as monitors of notebook computers, but also monitors of TVs to receive and display broadcast signals, and monitors of laptop computers.
Successful application of such LCDs to diverse image display devices depends on whether or not the LCDs can realize desired high picture quality including high resolution, high brightness, large display area, and the like, while maintaining desired characteristics of lightness, slimness and low power consumption.
Hereinafter, the structure of a conventional LCD device will be described with reference to the annexed drawings.
FIG. 1 is a plan view illustrating a conventional LCD device comprising a column spacer.
As shown in FIG. 1, a conventional LCD array region comprises gate lines 4 and data lines (not shown) that intersect each other to define pixel regions, thin film transistors (TFT) formed at respective intersections between the gate lines 4 and the data lines, and pixel electrodes 6 formed in the respective pixel regions. The array region further comprises column spacers 20 uniformly spaced apart from one another, to maintain a cell gap.
As shown in FIG. 1, each column spacer 20 is arranged in a region provided above the gate line 4. That is, the gate line 4 is arranged on a first substrate 1, a gate insulating film 15 is arranged over the entire surface of the first substrate 1 including the gate line 4, and a passivation film 16 is arranged on the gate insulating film 15.
Meanwhile, a black matrix layer 7 to shield non-pixel regions (i.e., portions where the gate lines and the data lines and the thin film transistors are formed) other than pixel regions is formed on the second substrate 2. In addition, a color filter layer comprising R, G and B color filters arranged at respective pixel regions is formed on the second substrate 2 including the black matrix layer 7, and a common electrode 14 is formed over the entire surface of the second substrate 2 including the color filter layer 8.
The column spacers 20 are formed on portions of the common electrode 14 corresponding to the gate lines 4. Accordingly, the first and second substrates 1 and 2 are joined together such that the column spacers 20 are arranged on the gate lines 4.
The column spacers 20 are formed in an array process performed on the first substrate 1 or the second substrate 2. The column spacers 20 are fixedly formed in the form of columns with a certain height on the predetermined substrate.
The column spacers 20 are fixed to specific positions and thus do not move when liquid crystals are dropped to form a liquid crystal layer. Advantageously, the column spacers do not inhibit the liquid crystals from flowing. However, the column spacers have a large area in contact with the corresponding substrate, thus disadvantageously causing display defects, e.g., touch defects.
Hereinafter, problems associated with LCDs employing ball spacers instead of column spacers will be illustrated.
FIG. 2 is a sectional view illustrating movement of a ball spacer. FIG. 3 is a sectional view illustrating a problem in which an alignment film arranged on a substrate that faces a ball spacer is damaged by movement of the ball spacer.
As shown in FIG. 2, in the liquid crystal display device using the ball spacer, the ball spacer 55 is arranged on the outermost surface of the structure including a black matrix layer 51, a color filter layer 52, an overcoat layer 53 and an alignment film 54 arranged on a second substrate 50 in this order.
The ball spacer 55 is dispersedly formed in a desired position on the second substrate 50 or the first substrate (not shown). Disadvantageously, the ball spacer 55 rolls on the substrate, where it is dispersed, due to its shape. Although formed in the desired position, the ball spacer 55 comes out of the position due to external force applied during the manufacturing process or impact applied in use, thus disadvantageously causing light leakage. That is, when the ball spacer 55 deviates from the original position, it comes out of the portion provided above the black matrix layer 51 and rolls toward the side of the portion. At this time, a height difference between the top of the ball spacer 55 which is arranged in the initial position, and the top of the ball spacer 55 which is arranged in the final position occurs, which is substantially comparable to the thickness of the black matrix layer 51. Such a height difference may cause variation in cell gap after the ball movement. In addition, the height difference involves problems in that an aperture ratio is decreased due to the ball spacer 55 arranged out of regions provided by the black matrix layer, and scattering occurs on the surface of the ball spacer 55 which moves into a pixel region. Furthermore, the ball spacer 55 arranged in the pixel region results in distorted orientation of liquid crystals, thus causing light leakage. In particular, a phenomenon in which light leakage is concentrated in a specific region due to the movement of the ball spacer is referred to as a “galaxy defect”.
In addition, as shown in FIG. 3, the structure provided on the second substrate 50 comprising the ball spacer 55 of FIG. 2 is reversed and faces the structure provided on the first substrate 60 to join the second substrate 50 to the first substrate 60.
The structure provided on the first substrate 60 comprises: a gate line 61 arranged in one direction; a gate insulating film 62 formed on the first substrate 60 including the gate line 61; a data line (not shown) formed on the gate insulating film such that the data line crosses the gate line 61 to define a pixel region; a passivation film 63 on the gate insulating film 62 including the data line; and a first alignment film 64 formed over the entire surface of the passivation film 63.
In addition, the movement of the ball spacer 55 may cause damage (e.g., tearing or rubbing distortion) to the surface of the second alignment film 64 that comes in contact with the ball spacer 55 in a dot-like area.
LCDs employing the afore-mentioned conventional ball spacers suffer from the following problems.
First, when column spacers are employed, they have a large area in contact with the substrate that faces the column spacers. For this reason, when a frictional force is applied to the column spacers by touch operations, the column spacers take a long time to return to their original state after they are pushed in one direction. Upon returning, display defects occur.
Second, when ball spacers are used instead of the column spacers in order to solve the problems such as touch defects, they tend to roll into pixel regions due to their mobility, causing additional defects e.g., display defects.
Third, when the ball spacer formed in only a specific local region is moved by an applied external impact, it passes a specific portion, while concentrically scratching the same, thus causing damage to the outermost surface (i.e., the alignment film) of the structure provided on the substrate that faces the ball spacer.